1. Field of the Invention
This invention relates to a cooling device for air-cooling moldings formed by a plastic molding machine, and a cooling method therefor.
2. Description of the Background Arts
Generally, for molding plastic by use of a plastic molding machine such as an injection molding machine, following steps are taken: plastics to be molded are supplied to a molding machine, before a die is closed; the plastics are heated to be plasticized in a cylinder of the injection molding machine and then the plasticized plastics are injected into the die from a nozzle, by a plunger being moved forward; after the die is kept at a pressure for a fixed time, the plunger is moved backward; and after some cooling time is given for the moldings in the die to be cooled down, the die is opened to take out the moldings formed into a predetermined shape.
In the molding steps of this kind, the process from closing the die to opening the die to take out the moldings is usually repeated as one production cycle. The time required for the one production cycle depends principally on injection time and cooling time. For achieving an improved productivity, acceleration of the production cycle, among others, shortening the cooling time, is being desired. For full cooling of the moldings in the die, the cooling time gets longer. On the other hand, for rapid cooling of the moldings in the die, a special cooling device is needed and the die will be complicated in structure and also must be made of materials capable of resisting an intense heat history caused by the rapid cooling, thus causing increase in the cost of production of the die. In addition, the rapid cooling introduces a problem that a dew condensation is caused on the surface of the die.
If the die is opened without fully cooling the moldings in the die, that may shorten the cooling time, but that can cause a problem that the moldings are deformed or warped after being taken out from the die.
There exists a prior art method according to which fans or equivalent are used in the process of transferring the moldings to air-cool the moldings taken out from the plastic molding machine, for the help of the cooling. But, such fans do not blow cooling air over the moldings from immediately after the moldings are taken out, so that they are not so useful for shortening the cooling time.